1. Field of the Invention
The present invention relates to a disc drive apparatus and a method for generating wobble information suitable for recording or reproduction of a disc recording medium on which recording tracks are formed, for example, in the form of grooves.
2. Description of the Related Art
A variety of discs, e.g., CDs-R (compact discs-recordable), CDs-RW (CDs-rewritable) and MDs (mini discs) have been developed and have spread as disc recording media.
In such CDS-R, CDs-RW and MDs, recording tracks are formed using grooves (guide grooves), and such grooves are wobbled to control the recording positions and the rotation of a spindle.
For example, such wobbles are formed based on frequency-modulated (FSK-modulated) signals according to information such as absolute addresses.
It is therefore possible to determine an address by extracting wobble information such as an absolute address from the groove.
For example, wobble information is extracted by an RF amplifier which generates necessary signals such as RF signals that are reproduction data, focus error signals FE and tracking error signals TE for servo control based on information of reflected light from spots of light projected upon a disc by a pickup.
The configuration of the RF amplifier depends on the method for controlling tracking of optical spots. For example, the well-known 3-spot method, push-pull system, DPP (differential push-pull) system and the like necessitate different configurations.
A method for generating wobble information in a conventional RF amplifier will now be described.
By way of example, a description will now be made on a method for generating wobble information in an RF amplifier which employs the DPP system as a tracking servo controlling system.
FIG. 9 shows a configuration of a DPP type RF processing circuit provided in a conventional disc drive apparatus.
In a disc drive apparatus in which tracking control is performed using a DPP system, a pickup generates a main spot for scanning a recording track and two side spots which are separate from the main spot.
Therefore, the pickup as a photo-detector 105 is provided with a main detector 151 that detects information of reflected light from the main spot and two side detectors 152 and 153 for detecting information of reflected light from the two side spots, respectively.
Referring to the actual locations of the detectors of the photo-detector 105, the side detectors 152 and 153 are respectively provided in front of and behind the main detector 151 in the direction of a track. In FIG. 9, however, the side detectors 152 and 153 are shown side by side for better understanding of the circuit configuration.
The main detector 151 is divided by a division line in a direction orthogonal to a track formed on a disc and a division line in parallel with the track into four detection areas A, B, C and D, and information of reflected light from the recording track is detected by the detection areas A, B, C and D. Pieces of information on reflected light detected by the detection areas A through D are converted by respective photoelectric conversion portions 154a, 154b, 154c and 154d into electrical signals A, B, C and D depending on quantities of reflected light and are output to the RF processing circuit.
In the present specification, the electrical signals detected by the detection areas A through D and converted by the photoelectric conversion portions 154a through 154d are referred to as xe2x80x9cdetection signals A through Dxe2x80x9d, respectively.
The detection signals A through D from the respective photoelectric conversion portions 154a through 154d are output to an adder 131 and a main sample-and-hold circuit 132 provided in the RF processing circuit.
The adder 131 adds the detection signals A through D from the respective photoelectric conversion portions 154a through 154d and outputs a resultant sum signal (A+B+C+D) as an RF signal or reproduction data signal.
For example, the main sample-and-hold circuit 132 samples and holds the detection signals A through D based on sample pulses input thereto during data recording and allows the detection signals A through D to pass through as they are without sampling and holding them in any other occasion.
A main matrix calculation/amplification circuit (main matrix amplifier) 133 performs various arithmetic processes for obtaining, for example, tracking error signals TE, focus error signals FE, wobble information WOB and the like from the signals A through D output by the main sample-and-hold circuit 132.
For example, it performs an arithmetic process (A+D)xe2x88x92(B+C) to obtain a tracking error signal TE and wobble information WOB before and during recording of data in a recording track and outputs the result of calculation as a main push-pull signal MPP.
Further, it performs an arithmetic process (A+C)xe2x88x92(B+D) to obtain a focus error signal FE.
For example, the main matrix amplifier 133 performs arithmetic processes (A+D) and (B+C) to obtain wobble information WOB after recording of data in a recording track and outputs the arithmetic outputs to AGC (automatic gain control) circuits 134a and 134b, respectively.
The AGC circuits 134a and 134b perform gain adjustment such that the amplitude levels of the arithmetic outputs (A+D) and (B+C) from the main matrix amplifier 133 become equal to each other and provides the output to a differential amplifier 135.
The differential amplifier 135 outputs the difference between the output signal (A+D) from the AGC circuit 134a and the output signal (B+C) from the AGC circuit 134b as (A+D)xe2x88x92(B+C). Therefore, the differential amplifier 135 outputs a push-pull signal whose gain has been adjusted by the AGC circuits 134a and 134b. 
Switching of a switch 136 is controlled depending on the operating state of the disc drive apparatus.
For example, the switch is controlled such that it is switched between a position after recording of data and a position before and during recording of data, and the output of the differential amplifier 135 is output to a band-pass filter (BPF) 137 after recording of data. Before and during recording of data, the main push-pull signal MPP from the main matrix amplifier 133 is output to the BPF 137.
The BPF 137 is a band-pass filter that allows wobble components having a central frequency of 22.05 kHz to pass through to eliminate other unnecessary frequency components. It extracts wobble components included in the push-pull signal input through the switch 136 to output wobble information WOB.
The side detectors 152 and 153 are divided into two detection areas E and F and G and H respectively by division lines in parallel with the track formed on the disc. Pieces of information of reflected light detected by the detection areas E through H are converted by photoelectric conversion portions 154e, 154f, 154g and 154h into respective output signals E, F, G and H which are in turn output to a side sample-and-hold circuit 138 of the RF amplifier.
In this case, the electrical signals detected by the detection areas E through H and converted by the photoelectric conversion portions 154e through 154h are referred to as xe2x80x9cdetection signals E through Hxe2x80x9d, respectively.
The side sample-and-hold circuit 138 receives the input of sample pulses similarly to the above-described main sample-and-hold circuit 132. For example, it samples and holds the detection signals E through H based on the sample pulses during recording of data and allows the detection signals E through H to pass through without sampling and holding them in any other occasion.
A side matrix amplifier 139 performs an arithmetic process (F+H)xe2x88x92(E+G) to obtain a tracking error signal TE from the output signals E through H of the side sample-and-hold circuit 138 and outputs the arithmetic result to a differential amplifier 140 as a side push-pull signal SPP.
The differential amplifier 140 obtains a differential signal (MPP-SPP) from the main push-pull signal MPP from the main matrix amplifier 133 and the side push-pull signal SPP from the side matrix amplifier 139 and outputs the same as a tracking error signal TE.
To satisfy demands for recording media having greater capacities, discs in the CD format having great capacities (e.g., discs having a capacity that is twice the capacity of existing CDs) have recently been developed by increasing recording density.
For convenience in description, such discs will be referred to as xe2x80x9chigh density discsxe2x80x9d, and discs in the CD format having conventional capacities will be referred to as xe2x80x9cstandard discsxe2x80x9d.
However, when it is attempted to extract wobble information from a high density disc in a disc drive apparatus employing the DPP system as described above that requires three spots, a problem arises in that the configuration of the optical system becomes complicated because changes must be made in the central frequency of laser light output by the laser light source provided in the pickup, the numerical aperture NA of the objective lens and so on.
Further, for example, when the density of tracks on a disc is increased without changing the specification of the optical system, crosstalk between adjoining tracks will create problems as described below.
FIGS. 10A and 10B show the relationship between spots of laser light emitted by a disc drive apparatus and track pitches. While FIGS. 10A and 10B show grooves G for recording tracks as being substantially straight, the grooves are wobbled in practice.
By way of example, FIG. 10A shows the relationship between laser spots and a track pitch of 1.6 xcexcm of a standard disc.
By way of example, FIG. 10B shows the relationship between laser spots and a track pitch of 1.1 xcexcm of a high density disc.
A comparison between the standard disc shown in FIG. 10A and the high density disc shown in FIG. 10B indicates that the track pitch of the high density disc is similar to or smaller than the diameter of a laser spot SPm.
Therefore, the high density disc is more vulnerable to crosstalk between adjoining tracks than the standard disc.
Especially when the grooves G are wobbled to record address information or the like using FSK modulation, the effect of crosstalk disturbs the phases of FSK-modulated signals, and resultant jitter components cause problems in that they disable reading of the address information and in that they make the spindle motor unstable.
The present invention has been conceived taking such problems into consideration. According to the invention, there is provided a disc drive apparatus capable of recording or reproducing a disc recording medium on which recording tracks are formed using grooves, which has light detecting means capable of obtaining a first push-pull signal from reflected light from a main spot of laser light and obtaining second and third push-pull signals from reflected light from two side spots of the laser light, a wobble signal component extractor for extracting wobble signal components in a recording track under a scan using the first push-pull signal, a crosstalk component signal generator for generating crosstalk component signals from adjacent tracks on both sides of the recording track using the second and third push-pull signals and a wobble information output unit for generating wobble information of the recording track from signals obtained by canceling the crosstalk component signals in the wobble signal components and for outputting the wobble information.
According to the invention, there is provided a method for generating wobble information from a disc recording medium on which recording tracks are formed using grooves, wherein wobble component signals in a recording track under a scan are extracted using a first push-pull signal obtained from reflected light from a main spot of laser light; and crosstalk component signals are generated from adjacent tracks on both sides of the recording track using second and third push-pull signals obtained from reflected light from two side spots of the laser light. Wobble information of the recording track is generated from signals obtained by canceling the crosstalk component signals in the wobble component signals.
According to the invention, crosstalk components generated by the second and third push-pull signals obtained from reflected light from two side spots of laser light are eliminated from the first push-pull signal including wobble components obtained from reflected light from a main spot. This makes it possible to reduce jitter components included in wobble information even when the wobble information is generated from a high density disc, for example.